1. Field of the Invention
The present invention relates to a continuously variable capacity type compressor. More particularly, the present invention relates to a wobble plate type compressor in which an inclination angle of the wobble plate is changed by a change in a differential level between a pressure in a crankcase interior and a pressure in a suction chamber, thereby automatically and continuously changing a discharge capacity under a condition wherein the pressure in the crankcase interior is kept at a predetermined level.
2. Description of the Related Art
In the wobble plate type compressor suitable for an air conditioning a vehicle, the inclination angle of the wobble plate is changed in accordance with the change of pressure in the suction chamber caused by a change in the cooling load in a vehicle, to change the refrigerant discharge capacity in accordance with the change in the cooling load in the vehicle. The pressure in the crankcase interior is kept at a predetermined level, and the wobble plate is inclined at a large inclination angle when the differential level between the pressure in the crankcase interior and the pressure in the suction chamber becomes low in response to a high cooling load in the vehicle, and is inclined at a small inclination angle when the differential level between the pressure in the crankcase interior and the pressure in the suction chamber becomes high in response to the low cooling load in the vehicle.
The inclination angle of the wobble plate is changed by a change in the pressure in the suction chamber. When the inclination angle is large, an operating distance is very small in a direction at a right angle to an axis of an drive shaft between the connecting pin and an end of a connecting rod for connecting the wobble plate with a piston. The piston is subjected to pressure in the crankcase interior and pressure in a discharge chamber at a compression stroke end (top dead center). Consequently, although there is a large differential level between the pressure in the crankcase interior and a pressure in the discharge chamber acting upon an under surface and a top surface of the piston, the moment value of the wobble plate in one direction about the connecting pin is very small. Thus, when this moment is in an equilibrium state, a differential level between the pressure in the crankcase interior and the pressure in the suction chamber acting upon an under surface and a top surface of another piston, which is at a suction stroke end (bottom dead center), is very small from the view point of moment equilibrium of the wobble plate. That is, the pressure in the suction chamber is substantially equal to the pressure in the crankcase interior.
When the inclination angle is small, the above-mentioned operating distance is much larger than the operating distance when the inclination angle is large. Thus, the moment about the connecting pin is in an equilibrium state when the pressure in the suction chamber is higher than the pressure in the crankcase interior, to oppose the differential pressure force between the pressure in the crankcase interior and the pressure in the discharge chamber, which force causes the moment of the wobble plate in the above mentioned one direction about the connecting pin.
As mentioned above, the pressure in the suction chamber becomes large in accordance with a decrease of the inclination angle of the wobble plate. A temperature of the air exhausted through an evaporator which absorbs heat from the air in the vehicle, has a relationship with the pressure in the suction chamber. Therefore, the temperature of the air exhausted through the evaporator becomes high in accordance with the decrease of the inclination angle of the wobble plate.
The rise in temperature of the air exhausted through the evaporator in accordance with the decrease of the inclination angle of the wobble plate is undesirable from the view point of the occupant of the vehicle, in particular when the temperature in a vehicle is changed suddenly by an external factor, such as by the effect of direct sunlight entering the vehicle when the compressor is operated in accordance with the low cooling load, the occupant of the vehicle becomes uncomfortable.